Radially-expandable PTFE tape-reinforced vascular grafts

ABSTRACT

A tape-reinforced tubular vascular graft formed of sintered fluoropolymer(s), such as expanded, sintered PTFE. The graft includes a base graft and a reinforcing tape applied thereto. The tape may be spirally wrapped about the graft or spirally wrapped into a tube about a cylindrical mandrel and then applied to the exterior of the graft. Radial shrinkage of the combined base graft and tape, or of the reinforcing tape tube, renders the vascular graft subsequently radially enlargeable by more than 5%, without tearing or breaking of the reinforcement tape layer of the graft. Radially enlargeable grafts of the present invention may be combined with various types of stents or anchoring systems, to form endovascular graft devices which are transluminally insertable and implantable within the lumen of a host blood vessel. Alternatively, radially enlargeable grafts of the present invention may be implanted by way of traditional surgical graft implantation techniques, without any radial enlargement of the graft at the time of implantation, so as to take advantage of the improved strength properties and suture-holding properties of the radially-shrunken tape-reinforced grafts of the present invention.

RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.09/912,006, now pending, which is a divisional of U.S. application Ser.No. 09/201,953, filed Dec. 1, 1998, entitled Process of Manufacturing aRadially Expandable PTFE Tape-Reinforced Vascular Graft, which is acontinuation of U.S. application Ser. No. 08/423,762, filed Apr. 17,1995, and issued on Jun. 24, 1997 as U.S. Pat. No. 5,641,373, entitledMethods of Manufacturing a Radially-Enlargeable PTFE Tape-ReinforcedVascular Graft.

FIELD OF THE INVENTION

The present invention relates generally to bioprosthetic vasculargrafts, and more particularly to a method of manufacturing radiallyenlargeable, tubular, tape-reinforced polytetrafluoroethylene (PTFE)vascular grafts.

BACKGROUND OF THE INVENTION

Polytetrafluoroethylene (PTFE) has been used for the manufacture ofvarious types of bioprosthetic vascular grafts, includingtape-reinforced, tubular grafts of the type frequently utilized toreplace or bypass a diseased or injured segment of blood vessel.

The expanded sintered PTFE from which the tubular base graft and thesurrounding reinforcement tape are formed typically has a microstructurecharacterized by the presence of dense areas known as “nodes”interconnected by elongate strands known as “fibrils”. The directionalorientation of fibrils is largely determined by the direction(s) inwhich the material was expanded prior to sintering thereof. The diameterand spacing of the fibrils is largely determined by the dynamics (i.e.,rate frequency and amount) of the expansion. The porosity of theexpanded sintered PTFE material is determined by the size of the spaceswhich exist between the fibrils, after the expansion step has beencompleted.

The sintering of the expanded PTFE is accomplished by heating theexpanded workpiece to a temperature above the melting point ofcrystalline PTFE. Typically, this is effected by heating the workpieceto a temperature of 350 deg.-375 deg. C. This sintering process ischaracterized by a transition of the PTFE polymer from a highlycrystalline form to a more amorphus form. Thus, the sintering process issometimes referred to as “amorphous locking” of the PTFE polymer. Thesintering process imparts significantly improved strength to the PTFEpolymer matrix, while also causing the polymer matrix to become harderand less stretchable.

In the tape-reinforced PTFE vascular grafts of the prior art, it hasbeen typical for the PTFE reinforcement tape to be wound spirally aboutthe outer surface of the base graft. Such orientation and positioning ofthe relatively thin, sintered, PTFE reinforcement tape about the outersurface of the base graft substantially precludes or severely limits theamount of radial stretching or radial expansion that the base graft mayundergo. Thus, the typical tape-reinforced tubular PTFE vascular graftof the prior art is incapable of undergoing more than a minimal amount(e.g., <5%) of radial stretching or radial expansion without tearing ofthe surrounding reinforcement tape.

The inability of tape-reinforced PTFE vascular grafts to undergo radialstretching or radial expansion has not interfered with the usualsurgical implantation of such grafts because, in the usual surgicalgraft implantation procedure, the graft is sized-matched to the hostblood vessel and is subsequently anastomosed into or onto the host bloodvessel. Thus, in traditional surgical implantation procedures, there hasbeen little or no need to effect radial stretching or radial expansionof the graft at the time of implantation.

Recently developed endovascular grafting procedures have, however,created a need for tape-reinforced tubular PTFE vascular grafts whichare capable of undergoing significant amounts of radial enlargement(i.e., radial expansion with resultant enlargement of the radialdimension of the graft). In these endovascular grafting procedures, thetubular vascular graft is typically passed through a catheter into thelumen of a deceased blood vessel and, thereafter, is deployed to an openor extended configuration within the lumen of the host blood vessel. Thegraft is then anchored to the surrounding blood vessel wall, therebyeffecting the desired endovascular placement of the graft within thelumen of the existing blood vessel. Thus, because it is necessary toinitially compact the graft and pass it through the lumen of arelatively small catheter, and to subsequently radially enlarge thegraft to its desired size and configuration, there exists a present needfor the development of a tape-reinforced tubular vascular graft which iscapable of undergoing in situ radial enlargement within the lumen of anexisting blood vessel.

SUMMARY OF THE INVENTION

The present invention comprises a method for increasing or improving theability of a tape-reinforced tubular graft (e.g., a graft comprising atubular base graft formed of expanded sintered PTFE and a quantity ofexpanded sintered PTFE reinforcement tape wrapped about the outersurface of the base graft) to undergo radial enlargement without tearingor breaking.

In accordance with the present invention, a radially enlargeabletape-reinforced tubular vascular graft may be formed by initiallymanufacturing the tape-reinforced graft in accordance with any suitablemanufacturing methodology, and subsequently radially shrinking thetape-reinforced graft to a decreased radial size. Such radial shrinkageof the tape-reinforced graft may be accomplished gradually, or inincremental steps, to minimize the likelihood of puckering of thetubular base graft as the surrounding reinforcement tape shrinks. Also,such radial shrinkage of the graft may be accomplished by any suitablepolymer shrinkage technique, including heat-induced shrinkage orchemical-induced shrinkage.

Further in accordance with the present invention, one or more rigidmandrel(s) may be inserted into the lumen of the tubular base graftduring the shrinkage process. In embodiments of the invention whereinthe shrinkage process is accomplished in incremental or step wisemanner, a single mandrel of adjustable diameter, or multiple mandrels ofincrementally smaller diameter, may be utilized to effect the desiredgradual, incremental or step-wise shrinkage of the graft.

Further in accordance with the invention, the desired shrinkage of thetape-reinforced graft may be accomplished by passing the tape-reinforcedgraft through a sizing dye to accomplish the desired radial shrinkagethereof.

Still further in accordance with the invention, the radially enlargeabletape-reinforced PTFE vascular graft may be alternatively formed byinitially wrapping the expanded sintered PTFE reinforcement tape aboutthe rigid mandrel to create a tape-tube which is devoid of any tubularbase graft. The tape-tube is then radially shrunken, in accordance withthe present invention, and the radially shrunken tape tube issubsequently applied to the outer surface of a relatively small-diametertubular base graft. The tubular base graft and the surrounding shrunkentape-reinforcement may then be radially enlarged in accordance with thepresent invention, without tearing or breaking of the reinforcementtape.

Still further in accordance with the present invention, any embodimentof the radially enlargeable tape-reinforced tubular PTFE grafts of thepresent invention may be provided with external support filaments orbeading to provide structural support to the graft, and to preventindentation or kinking of the graft lumen when implanted. Such supportfilaments or beading may be formed of PTFE or any other suitablematerial.

Further objects and advantages of the invention will become apparent tothose skilled in the art upon reading and understanding of the followingdetailed description, and consideration of the accompanying figures.

Brief Description of the Drawings

FIG. 1 is a block diagram showing a presently preferred method formanufacturing a radially enlargeable, tape-reinforced, tubular vasculargraft of the present invention.

FIG. 2 is block diagram showing an alternative method for manufacturinga radially enlargeable tape-reinforced tubular vascular graft of thepresent invention.

FIG. 3 is a block diagram showing a presently preferred method forendovascular implantation and in situ radial expansion of atape-reinforced vascular graft of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description and the accompanying drawings towhich it refers are provided for purposes of describing and illustratingthe presently preferred embodiments of the invention, and are notintended to limit the scope of the invention in any way.

1. Method for Manufacturing a Radially Expandable Tape-Reinforced, PTFEVascular Graft

As shown in the block diagram of FIG. 1, the preferred method ofmanufacturing a tape-reinforced vascular graft of the present inventioninvolves separate preparation of a) an expanded, sintered, tubular PTFEbase graft and b) an expanded, sintered PTFE reinforcement tape.

The PTFE reinforcement tape is then spirally wound about and laminatedor fused to the outer surface of the tubular base graft, thereby formingthe desired tape-reinforced vascular graft.

Thereafter, in accordance with the present invention, the sintered,tape-reinforced, tubular vascular graft is radially shrunken to areduced radial dimension, such that the graft may be subsequentlystretched or expanded to or near its original (pre-shrinkage) radialdimension.

A. Preparation of the Tubular Base Graft

The preferred method for preparing the expanded, sintered PTFE tubularbase graft is shown in FIG. 1.

i.) Preparation of Paste

The manufacture of the tubular base graft begins with the step ofpreparing a PTFE paste dispersion 10 for subsequent extrusion. This PTFEpaste dispersion may be prepared by known methodology whereby a fine,virgin PTFE powder (e.g., F-104 or F-103 Virgin PTFE Fine Powder, DakinAmerica, 20 Olympic Drive, Orangebury, N.Y. 10962) is blended with aliquid lubricant, such as odorless mineral spirits (e.g., Isopar.RTM.,Exxon Chemical Company, Houston, Tex. 77253-3272), to form a PTFE pasteof the desired consistency.

ii.) Extrusion of Tube

The PTFE-lubricant blend dispersion is subsequently passed through atubular extrusion dye to form a tubular extrudate 12. The extrudateformed in this step of the method has a diameter or cross-dimensionwhich is approximately the same as the final diameter or cross-dimensiondesired of the graft after it has been implanted and subjected toin-situ radial expansion in accordance with the present invention.

iii.) Drying

The wet tubular extrudate is then subjected to a drying step 14 wherebythe liquid lubricant is removed. This drying step 14 may be accomplishedat room temperature or by placing the wet tubular extrudate in an ovenmaintained at an elevated temperature at or near the lubricants drypoint for a sufficient period of time to result in evaporation ofsubstantially all of the liquid lubricant.

iv.) Expansion

Thereafter, the dried tubular extrudate is longitudinally expanded 16 orlongitudinally drawn at a temperature less than 327 deg. C. andtypically in the range of 250 deg.-326 deg. C. This longitudinalexpansion 16 of the extrudate may be accomplished through the use ofknown methodology, and may be implemented by the use of a device knownas a batch expander. Typically, the tubular extrudate is longitudinallyexpanded by an expansion ratio of more than two to one (2:1)(i.e., atleast two (2) times its original length).

v.) Sintering

After the longitudinal expansion step has been completed, the tubularextrudate is subjected to a sintering step 18 whereby the extrudate isheated to a temperature above the sintering temperature of PTFE (i.e.,350 deg.-370 deg. C.) to effect amorphous-locking of the PTFE polymer.The methodology used to effect the sintering step, and the devices usedto implement such methodology, are known in the art.

Completion of the sintering step 18, marks the completion of thepreparation of the expanded, sintered PTFE base graft.

B. Preparation of Reinforcement Tape

i.) Preparation of Paste Dispersion

In accordance with preferred method shown in FIG. 1, the preparation ofthe expanded sintered PTFE reinforcement tape includes the initialpreparation of a PTFE paste dispersion 20. The PTFE paste dispersionprepared in this step 20 may be prepared in the same manner as describedhereabove for preparation of the PTFE paste dispersion 10 used to formthe tubular base graft.

ii.) Extrusion of Film

The PTFE paste dispersion 20 is subsequently passed through the filmextrusion dye to form a wet film extrudate 22. The wet film extrudate istaken up or wound upon a rotating core so as to form a roll of the wetfilm extrudate.

iii.) Calendaring

The wet film extrudate is subsequently unrolled and subjected to aninitial cold (i.e., <100 deg. C.) calendaring step 24 by passing thefilm through at least one set of opposing stainless steel calendaringrollers having an adjustable gap thickness therebetween. The calendaringrollers are preferably maintained at a temperature between roomtemperature and 60 deg. C. The width of the wet extrudate is heldconstant as it passes through these calendaring rollers. The thicknessof the wet film extrudate is reduced to its desired final thickness(e.g., 0.004-0.005 inches) while the width of the film is maintainedconstant. It will be appreciated that, since the width of the film ismaintained constant, the passage of the film through the calendaringmachine will result in a longitudinal lengthening of the film. Theamount of longitudinal lengthening will be a function of the decrease infilm thickness which occurs as the film passes between the calendaringrollers.

One example of a commercially available calendaring machine useable forthis purpose is the small Killion 2 Roll Stack, (Killion Extruders,Inc., Cedar Grove, N.J. 07009.)

iv) Drying

Thereafter, the wet film is subjected to a drying step 26. This dryingstep may be accomplished by permitting or causing the liquid lubricantto evaporate from the matrix of the film. Such evaporation of the liquidlubricant may be facilitated by passing the film over a drum or rollerwhich is maintained in an elevated temperature sufficient to cause theliquid lubricant to filly evaporate from the film matrix.

v) Expansion

Separately, or concurrently with the drying step 26, the film issubjected to an expansion step 28. Such expansion step comprisesexpanding the PTFE film in at least one direction (e.g.,longitudinally). Such expansion of the film serves to a) increase theporosity of the film, b) increase the strength of the film, and c)orient the PTFE fibrils in the direction of the axis of expansion.

This expansion step 28 is typically carried out with some heating of thefilm during such expansion, but such heating does not exceed thecrystalline melting point of the PTFE polymer.

vi) Sintering

After the drying step 26 and expansion step 28 have been completed, thefilm is subjected to a sintering step 30 wherein the film is heated to atemperature above the melting point of PTFE to accomplish sintering oramorphous locking of the PTFE polymer. This sintering step 30 may becarried out by passing the film over a drum or roller which ismaintained at a high surface temperature (e.g., 350 deg.-420 deg. C.) tocause the desired heating of the PTFE film above the melting point ofthe PTFE polymer for a sufficient period of time to effect the desiredsintering of the film.

C. Wrapping and Lamination of the Reinforcement-Tape onto the Base Graft

After the sintered PTFE base graft and sintered PTFE reinforcement tapehave been separately prepared, the tape-reinforced tubular graft isfabricated by spirally wrapping the PTFE reinforcement tape onto theouter surface of the tubular base graft 32. Thereafter, the tape islaminated or fused onto the outer surface of the graft 34.

Typically, in carrying out these steps (i.e., winding of the tape 32 andlamination 34 of the method, a first rigid stainless steel rod ormandrel, having an outer diameter substantially the same as the lumenaldiameter of the sintered expanded tubular extrudate (i.e., the basegraft) is inserted into the lumen of the base graft. Thereafter, themandrel-borne sintered PTFE tubular base graft is rotated or spun aboutits longitudinal axis while the strips of expanded, sintered PTFEreinforcement tape are laid on the outer surface of the base graft,thereby spirally wrapping the tape onto the base graft to form thedesired tape-reinforced graft structure. The ends of the tape reinforcedgraft are then affixed to the first mandrel by way of wire ligatures,thereby preventing the tape-reinforced graft from longitudinalshortening.

The mandrel-borne, tape-reinforced graft is then placed in an oven andheated to a temperature of approximately 355 deg.-375 deg. C. for aperiod of approximately 10-60 minutes to cause the sintered PTFEreinforcement tape to become laminated to the outer surface of thesintered PTFE base graft.

The presence of the first rigid mandrel within the lumen of thetape-reinforced graft prevents the tape-reinforced graft from undergoingradial shrinkage or contraction during this lamination step. Also, thewire ligatures affixing the ends of the tape-reinforced graft to therigid mandrel prevent the graft from undergoing longitudinal shrinkageor shortening during this lamination step.

D. Radial Shrinkage of the Tape-Reinforced Graft

After the tape has been laminated onto the outer surface of the basegraft to form the desired tape-reinforce graft structure, thetape-reinforced graft is subjected to radial shrinkage 36. This radialshrinkage step 36 may be carried out in one or more increments orstages.

In accordance with the preferred method, the radial shrinkage of thegraft may be carried out by initially removing the wire ligatures whichheld the graft to the first rigid mandrel, and removing the first rigidmandrel from the lumen of the graft.

Thereafter, a second rigid mandrel, having an outer diameter which issmaller than the outer diameter of the first rigid mandrel, is insertedthrough the lumen of the graft, and the ends of the graft are affixed,by way of wire ligatures, to the second rigid mandrel.

Thereafter, the second rigid mandrel and the tape-reinforced graftdisposed thereon are placed back in the oven at a temperature of 355deg. C. for a period of approximately 10 minutes to cause the graft toundergo radial shrinkage until the lumenal diameter of the graft hasbecome substantially the same as the outer diameter of the second rigidmandrel.

Thereafter, the wire ligatures are removed and the second rigid mandrelis extracted from the lumen of the graft.

A third rigid mandrel, having an outer diameter which is smaller thanthe outer diameter of the second rigid mandrel, is then inserted throughthe lumen of the graft and wire ligatures are utilized to affix the endsof the graft to the third rigid mandrel.

Thereafter, the third rigid mandrel, along with the tape-reinforcedgraft disposed thereon, is placed in an oven at a temperature of 355deg. C. for a period of approximately 10 minutes to cause the graft toundergo further radial shrinkage until the lumenal diameter of the graftis substantially the same as the outer diameter of the third rigidmandrel.

The above-described shrinkage steps may be repeated consecutively usinga number of progressively smaller rigid mandrels to effect incremental(e.g., staged) radial shrinkage of the graft. Care is taken to firmlyaffix the ends of the graft to each rigid mandrel prior to shrinkagethereof, so as to prevent the graft from undergoing longitudinalshrinkage or longitudinal shortening during the radial shrinkageprocess.

Although any suitable number of incremental shrinkage steps may beutilized, it is expected that in most applications the desired radialshrinkage of the graft will be accomplished with the use of no more thanfive (5) progressively smaller rigid mandrels.

For example, if it is desired to manufacture a tape-reinforced tubulargraft which will have a lumenal diameter, when fully expanded, of 0.5inches, it will be desirable to initially manufacture thetape-reinforced graft structure to have such 0.5 inch lumenal diameterprior to shrinkage thereof. Thereafter, the tape-reinforced graftstructure may be subjected to incremental shrinkage of reduced diametermandrels such as shown in the following example: Preparation of aRadially Enlargeable Graft Having an OD of 0.3 Inches MANDREL NO MANDRELOUTER DIAMETER 1  0.5 inch 2 0.45 inch 3  0.4 inch 4 0.35 inch 5  0.3inch

Thus, by incrementally shrinking the graft onto the outer surfaces ofthe five (5) shrinking mandrels listed hereabove, the lumenal diameterof the graft will be reduced from an initial lumenal diameter of 0.5inches to a final lumenal diameter of 0.3 inches.

The tape-reinforced graft described hereabove, having a lumenal diameterof 0.3 inches, may then be re-expanded to a fully expanded diameter ofapproximately 0.5 inches—the same as its original diameter prior toshrinkage.

The incremental or step-wise shrinkage of the graft is for the purposeof preventing puckering or wrinkling of the graft as may occur if alarge amount of radial shrinkage is effected in a single step. Althoughthis incremental or step wise shrinkage is described hereabove withreference to a batch manufacturing method whereby individual segments ofthe graft material are placed on progressively smaller rigid mandrels orrods, it will be appreciated that the method of the present inventionmay also be carried out by various continuous techniques whereby theradial shrinkage of the graft will occur gradually, without puckering orwrinkling of the tubular base graft. For example, a continuous elongatetubular tape-reinforced graft may be drawn longitudinally over thesurface of a gradually tapered or gradually narrowed rigid mandrel whileheat is applied thereto to bring about the desired gradual radialshrinkage of the graft as it passes over the outer surface of thetapered or narrowed rigid mandrel. Alternatively, a segment oftape-reinforced tubular graft material may be initially placed on asingle mandrel of adjustable or shrinkable diameter such that themandrel will decrease or shrink in diameter as the graft shrinks indiameter.

It is intended that the present invention, as claimed herebelow, includeany and all such continuous embodiments and/or adjustable/shrinkablemandrel embodiments of the method, as well as the specificbatch-preparation method described hereabove. The radially shrunkentape-reinforced tubular PTFE grafts formed by the above-set-forth methodmay be cut into desired lengths, sterilized by gas or other suitablesterilization method(s), and packaged for distribution and subsequentimplantation in a mammalian host.

It will be appreciated that the radially shrunken tape-reinforced PTFEvascular grafts of the present invention may be used in applicationswherein they are anastomosed into a host blood vessel by known opensurgical techniques, without being subjected to radial enlargement atthe time of implantation of the graft. In these applications, oneadvantage which may be achieved through the use of the radially shrunkengraft material is improved suture holding strength and a decreasedlikelihood of suture tear through when the ends of the graft areanastomosed to the host blood vessel.

Also, the radially shrunken tape-reinforced PTFE grafts of the presentinvention may be used in a variety of endovascular applications whereinthey will be radially expanded or radially dilated at the time ofimplantation. In this regard, the radially expandable vascular grafts ofthe present invention may be used in conjunction with various presentlyknown or hereafter invented anchoring devices, stents, or other supportsystems for affixing and holding the graft at its desired positionwithin the lumen of a mammalian blood vessel.

F. Additional External Reinforcement

In some applications, it is desirable for the grafts manufactured by themethod of the present invention to include an external reinforcementmember, such as a PTFE filament wound spirally about and fused to theouter surface of the tape-reinforced graft. The type(s) of PTFEfilaments used to form such reinforcement member are typicallysufficiently stretchable to accommodate and undergo the desired amountof radial expansion or radial stretching of the tape-reinforced graft.Thus, it is possible to apply and affix such PTFE filament reinforcementmember by traditional methods, after the tape-reinforced graft has beenradially shrunk.

In accordance with the invention, in embodiments where it is desired toprovide a PTFE reinforcement filament on the outer surface of the graft,the radially shrunken tape-reinforced graft provided at the end of theradial shrinkage step 36 may be positioned on a rigid mandrel having anouter diameter equal to the shrunken inner diameter of the graft lumen.Thereafter, a sintered PTFE monofilament bead, such as that commerciallyavailable as PTFE beading, (Zeus Industrial Products, Inc., Orangeburg,S.C.) is spirally wound about the outer surface of the tape-reinforcedtubular graft 38.

Thereafter, the mandrel-borne tape-reinforced vascular graft having thePTFE filament spirally wound thereon is placed in an oven and heated toa temperature which is sufficient to fuse or laminate the PTFEreinforcement filament to the outer surface of the tape-reinforced graft40.

It will be appreciated that alternative methods of fusing the beading tothe outer surface of the graft may also be employed.

When so manufactured, the PTFE filament applied to the outer surface ofthe graft will undergo radial expansion or radial stretchingconcurrently with the remainder of the tape-reinforced graft prepared inaccordance with the above-described method of the present invention.

2. Alternative Method for Forming the Radially EnlargeableTape-Reinforced Graft

As an alternative to the above-described method, wherein the entiretape-reinforced graft (i.e., the reinforcement tape in combination withthe tubular base graft) is subjected to radial shrinkage, the radiallyexpandable tape-reinforced graft of the present invention may also bemanufactured by an alternative method wherein only the reinforcementtape is subjected to radial shrinkage, and such radially shrunkenreinforcement tape is subsequently applied to a relatively smalldiameter tubular base graft such that the base graft-reinforcement tapecombination is capable of subsequently undergoing radial enlargementwithout tearing or breaking of the reinforcement tape.

This alternative method is shown in the block diagram of FIG. 2.

i. Preparation of Small Diameter Base Graft

A relatively small diameter tubular base graft is prepared of expandedsintered PTFE material by the same steps 10 through 18 as describedhereabove. However, in this method, the tubular base graft is of adiameter which is equal to the desired diameter of the finaltape-reinforced graft after radial shrinkage thereof. The tubular basegraft is preferably a thin walled or ultra-thin walled graft capable ofundergoing more than 5% radial enlargement without tearing or breaking.

ii) Preparation of PTFE Reinforcement Tape Tube

Also, in this method, a quantity of expanded sintered PTFE reinforcementtape is prepared by the same steps 20 through 30 as described hereabove.Thereafter, the expanded sintered PTFE reinforcement tape is used toprepare a “tape-tube” and such tape tube is subsequently subjected toradial shrinkage, then applied to the outer surface of the smalldiameter thin or ultra-thin walled base graft.

Specifically, as shown in FIG. 2, the tape-tube may by prepared byinitially wrapping 80 the expanded sintered PTFE reinforcement tapearound a rigid mandrel in overlapping or otherwise abuttingconvolutions, to form an elongate, tubular tape configuration. Themandrel-borne tape is then placed in an oven or otherwise heated to atemperature which causes the convolutions of tape to laminate or fuse toone another, thereby forming a tape-tube 82.

Also, the tape-tube may be prepared by the methodology disclosed in U.S.Pat. No. 5,207,960 (Moret de Rocheprise) entitled, METHOD FOR THEMANUFACTURE OF THIN TUBES OF FLUORINATED RESIN, PARTICULARLY OFPOLYETRAFLUOROETHYLENE.

iii) Radial Shrinkage of Tape-Tube

The tape-tube is then subjected to radial shrinkage, by any suitablemethod, including any of the heat-induced or chemical-induced shrinkagemethods described herein. Since the tape-tube is devoid of any internalbase graft, it may be unnecessary to utilize the gradual or incrementalshrinkage described hereabove, as such gradual or incremental shrinkageis primarily intended to avoid puckering or infolding of the base graft.In this regard, the tape tube may simply be placed on a small diametermandrel, such mandrel having a diameter substantially equal to theintended diameter of the tape-tube after shrinkage thereof. The ends ofthe tape-tube may be affixed to the mandrel to prevent longitudinalshrinkage or longitudinal shortening of the tape-tube during theshrinkage process. Thereafter, the small diameter mandrel and thetape-tube affixed thereto may be heated to a temperature which causesthe tape tube to shrink to the diameter of the mandrel. Thereafter, thetape-tube is removed from the small diameter mandrel and utilized forsubsequent fabrication of the desired radially enlargeabletape-reinforced graft.

iv) Fabrication of Tape-Reinforced Graft

The radially enlargeable tape-reinforced graft is fabricated byinserting the previously prepared small diameter tubular base graft intothe lumen of the radially shrunken tape-tube 86.

v) Fusion of Tape-Tube to Base Graft

Thereafter, the tape-tube/base graft combination is heated or otherwisetreated to cause the tape-tube to fuse to the outer surface of the basegraft, 88. Such fusion of the tape-tube to the outer surface of the basegraft, results in the formation of the desired radially enlargeabletape-reinforced graft.

In a variation of the above, described alternative method, thereinforcement tape may be longitudinally shrunk, without being formedinto a tape-tube as described hereabove. Such longitudinally shrunkentape may then be spirally wrapped around, and laminated to a relativelysmall diameter base graft—in accordance with the above-describedwrapping and lamination methods, thereby forming a radially enlargeabletaps-reinforced graft.

3. Method for Endoluminal Placement and In Situ Radial Expansion of theGrafts

The radially enlargeable vascular grafts of the present invention, asdiscussed hereabove, may be utilized in the manufacture of endovasculargrafting systems which are deployable into the lumen of a blood vesselthrough a catheter or other tubular introducer and subsequently radiallyexpandable such that the lumen of the graft will approximate the lumenalsize of the blood vessel wherein the graft is disposed, and the graftwill become anchored or affixed to the surrounding blood vessel wall.

It will be appreciated that in many such endovascular applications, itwill be desirable to utilize the radiallyenlargeable tape-reinforcedvascular graft of the present invention in conjunction with one or morea) anchoring mechanisms, b) stents or c) other fixation devices, for thepurpose of securing and affixing the graft to the surrounding bloodvessel wall. Examples of endovascular graft affixation devices, stentsand/or other means which may be used for supporting or affixing anendoluminally positioned tubular graft of the present invention aredescribed in the following United States and foreign patents/patentpublications: U.S. Pat. No. 4,733,665 (Palmaz), U.S. Pat. No. 4,776,337(Palmaz), U.S. Pat. No. 5,037,392 (Hillstead), U.S. Pat. No. 5,116,318(Hillstead), U.S. Pat. No. 5,135,536 (Hillstead), U.S. Pat. No. 5,21,658(Clouse), U.S. Pat. No. 5,219,355 (Parodi et al.), U.S. Pat. No.5,275,622 (Lazarus et al.), U.S. Pat. No. 5,282,824 (Gianturco), U.S.Pat. No. 5,292,331 (Boneau), U.S. Pat. No. 5,330,500 (Song), U.S. Pat.No. 5,354,308 (Simon et al), U.S. Pat. No. 5,360,443 (Borone et al),U.S. Pat. No. 5,015,253 (MacGregor), U.S. Pat. No. 5,171,262(MacGregor), U.S. Pat. No. 5,061,275 (Wallsten et al.), U.S. Pat. No.5,282,860 (Matsuno et al.), U.S. Pat. No. 5,290,305 (Inoue), U.S. Pat.No. 5,304,200 (Spaulding), U.S. Pat. No. 5,306,286 (Stack et al.),DT197808 (Choudhury), SU 1217-402-A (Khark), EP 466-518-A (Harrison etal.), EP 579523-A1 (Cottenceau J., et al.), 2,189,150-A (Medinvent), andWO 90/02641 (Bowald et al.).

Also, in endovascular applications wherein it is desired to radiallyenlarge the graft in situ, it will be appreciated that various types ofexpansion apparatus may be used to cause the desired radial expansion orradial stretching of the graft. In particular, a generally cylindricalballoon may be formed on the outer surface of a catheter and insertedwithin the lumen of the shrunken graft during or after placement of thegraft within the lumen of the host blood vessel. Thereafter, the balloonmay be inflated to cause controlled radial expansion of the graft. Afterbeing fully radially enlarged, the graft may be affixed or anchored tothe surrounding blood vessel wall.

The general preferred method for endovascular placement and in situ postexpansion of a radially expandable tape-reinforced tubular PTFE vasculargraft of the present invention is shown in FIG. 3.

Initially, the radially enlargeable tape-reinforced tubular vasculargraft is mounted on a stent or graft anchoring system 50 to facilitateaffixation or anchoring of the graft at its desired location within thelumen of a host blood vessel.

Thereafter, the graft (with the accompanying stent or anchoring system)may be positioned over an inflatable balloon formed on a ballooncatheter 52. The balloon will be sized and configured relative to thegraft and its accompanying stent or anchoring system, such thatsubsequent inflation of the balloon will cause the desired radialexpansion of the graft. Typically, for standard tubular vascular graftsof generally round cylindrical configuration, a cylindrical balloonconfiguration will be used.

Thereafter, a guide catheter is inserted 54 into the vasculature andadvanced to a point where the distal end of the guide catheter islocated adjacent to the intended implantation site. Such guide catheterinsertion step 54 may be accomplished percutaneously, as by way of theSeldinger Technique.

The balloon catheter having the graft (with its accompanying stent oranchoring system) positioned thereon is either a) prepositioned withinthe lumen of the guide catheter and inserted concurrently with the guidecatheter insertion 54 or b) advanced through the lumen of the guidecatheter after the guide catheter has been inserted 54 and advanced toits desired location within the vasculature. By either method, theballoon catheter (having the graft and its accompanying stent/anchoringapparatus mounted therein) is advanced through the lumen of the guidecatheter 56.

The graft (with its accompanying stent or anchoring system) is thusadvanced out of the distal end of the guide catheter and is positioned58 at its intended implantation site within the vasculature.

Thereafter, the balloon is inflated to cause radial expansion 60 thegraft at its intended implantation site. Such radial expansion of thegraft may also facilitate activation or deployment of the stent oranchoring system such that the expanded graft will become anchored tothe surrounding blood vessel wall. In some instances, the anchoringapparatus will consist of piercing members or protrusions which becomeinserted into the surrounding blood vessel wall as the graft is radiallyexpanded. In other instances, the anchoring system could consist of astent or other device which frictionally engages the wall of the bloodvessel as the graft is radially expanded. Irrespective of the particulartype of anchoring system or stent utilized, it is desirable that the actof radially expanding the graft by inflation of the balloon willconcurrently actuate the intended anchoring or placement mechanism so asto hold the graft at its intended implantation site.

It will be appreciated that any appropriate radiological or otherlocating device or apparatus may be used to guide and verify thepositioning of the graft at its desired implantation site 58. Tofacilitate this, the graft may be provided with one or more radialopaque markers to render the graft easily visible by radiographic means.In many applications, it is expected that one or more angioscopes willalso be positioned within the blood vessel, adjacent the intendedimplantation site of the graft, so as to enable the operator to visuallyguide and verify the positioning 58, expansion 60 and accompanyinganchoring of the graft at its intended implantation site.

After the graft has been radially expanded to its desired size andappropriately anchored or implanted at its intended implantation site,the balloon may be deflated and the balloon catheter, as well as theaccompanying guide catheter may be withdrawn 62.

By the above-described method, a radially expandable graft of thepresent invention may be percutaneously, transluminally implanted withina host blood vessel without the need for open surgical excision of theblood vessel.

Although the foregoing has provided a description of a preferred methodfor transluminal endovascular placement of a radially enlargeable graftof the present invention, it will be appreciated that the grafts of thepresent invention may also find utility in traditional open surgicalimplantation methods wherein it is desired to provide a graft havingimproved strength and improved resistance to suture pull-through. Inthis regard, radially shrunken endovascular grafts of the presentinvention may be provided for surgical implantation by traditional opensurgical techniques wherein a radially shrunken vascular graft of thepresent invention is anastomosed into the host blood vessel to replaceor bypass a diseased, or damaged segment of the vessel. In this regard,the shrunken size of the graft will be matched to the size of the hostblood vessel, and the graft will be sutured in place without effectingany radial enlargement of the graft. The radial shrinkage of the graftwhich took place during the manufacturing process will have impartedsubstantial improvements to the overall strength and suture holdingproperties of the graft, even though no radial enlargement of the graftis effected at the time of implantation.

Although the invention has been described herein with reference tocertain preferred embodiments, it will be appreciated that theabove-described embodiments may be altered, modified or changed in manydifferent ways without departing from the intended spirit and scope ofthe invention. For example, the radial shrinkage of the reinforcementtape, or of the entire tape-reinforced tubular graft, may beaccomplished by any suitable method other than the heat-inducedshrinkage methods described specifically herein, including the use ofany suitable chemical shrinkage technique whereby exposure of thereinforcement tape and/or the entire tape-reinforced graft to aparticular chemical will cause the reinforcement tape and/or the entiretape-reinforced graft to undergo the desired radial shrinkage. It isintended that all such modifications changes or alterations to theabove-described methods be included within the scope of the followingclaims.

1. A radially expandable tape-reinforced tubular vascular graft,comprising: a tubular PTFE base graft having a diameter; and areinforcing tape wrapped into a spirally wound tube, the reinforcingtape being initially formed by a preliminary step of expansion so as tohave an expanded porosity, the tube having an expanded diameter largerthan the diameter of the base graft; and wherein: the reinforcing tapetube is radially shrunk from the expanded diameter to a reduced diameterand applied to the outside of the tubular PTFE base graft to form theradially expandable tape-reinforced tubular vascular graft suitable forintroduction and expansion in the vasculature, the tape tube in thevascular graft prior to expansion having a porosity less than itsexpanded porosity.
 2. The vascular graft of claim 1, wherein thepreliminary step of expansion of the reinforcing tape is accomplished byheating the tape to a temperature of less than the crystalline meltingpoint of the PTFE and longitudinally expanding it along its lengthdirection.
 3. The vascular graft of claim 2, wherein the reinforcingtape is sintered after the preliminary step of expansion and prior tobeing applied to the outside of the tubular PTFE base graft.
 4. Thevascular graft of claim 1, wherein the reinforcing tape is fused byheating to the tubular PTFE base graft after being applied to theoutside thereof.
 5. The vascular graft of claim 1, wherein the expandedreinforcing tape tube is radially reduced in size by heating.
 6. Thevascular graft of claim 5, wherein the expanded reinforcing tape tube isradially reduced in size by positioning it around a first cylindricalmandrel having an outside diameter smaller than the inside diameter ofthe tube and heating to a sintering temperature.
 7. The vascular graftof claim 1, wherein the expanded diameter of the tube is at least 5%greater than the reduced diameter.
 8. The vascular graft of claim 1,wherein the expanded diameter of the tube is at least 66% greater thanthe reduced diameter.
 9. The vascular graft of claim 1, furtherincluding an anchoring mechanism coupled to the vascular graft forsecuring the graft to a vascular wall.
 10. The vascular graft of claim1, further including a stent coupled to the vascular graft for securingthe graft to a vascular wall.
 11. The vascular graft of claim 1, furtherincluding a reinforcing PTFE filament spirally wound around thereinforcing tape.